Use of Electrical Resistivity Tomography (ERT) for Detecting Underground Voids on Electrical Pylon Installation Sites: Case Studies from Labé Prefecture, Republic of Guinea

Abstract

AbstractThis study was carried out within the framework of the Gambia River Basin Development Organization Energy Project (OMVG), which brings together Gambia, Guinea, Guinea-Bissau and Senegal. The construction of a high voltage interconnection network fed by a hydro-electricity power station to supply power to OMVG member states must be done on stable ground. During the construction of the installation pits for the pylons in Labé Prefecture, cavities in the geological formations were discovered on the initial planned route. Regarding to geotechnical context of subsurface cavities risk it is mandatory to know their exact location in study areas to reduce the potential degree of risk. A field study was conducted to investigate the lithology, as well as in detecting the presence of apparent faults. Geophysical data was collected using Two Dimensional ERT with different electrode spacing to delineate associated subsurface cavities on each site and each cavity respectively. The target depth was 20 m. The result shows that the observed cavities were because of the dissolution of certain minerals constituting the weathering crust due to the infiltration and the seasonal variation in the level of the watercourses. The cavities were almost entirely empty such as in the cases of pylons 213 and 210 indicated that the weathering crust is due to the groundwater infiltration and the seasonal variations in the river flow level. The finding of this study showed that the ERT method have a good applicability in the detection of underground cavities in the study area.